This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-53483 filed in Japan on Mar. 4, 2008, the entire contents of which are herein incorporated by reference.
The present technology relates to a development apparatus that uses a two-component developer containing toner and a carrier, and an image forming apparatus using the same.
In general, processes such as charging, exposure, developing, transfer, cleaning, charge removal, and fixing are performed in an image forming apparatus using an electrostatic photographic image forming method. In a process of forming an image in such an image forming apparatus, for example, the surface of an image carrier such as a photosensitive drum that is driven to rotate is uniformly charged by a charging apparatus, and a laser beam is irradiated onto the surface of the charged image carrier by an exposing apparatus. Then, an electrostatic latent image is formed on the surface of the image carrier. Subsequently, a developer carrier such as a development roller, for example, of the development apparatus transports developer to a development nip portion between the developer carrier and the image carrier. The electrostatic latent image formed on the image carrier is developed by the developer transported to the development nip portion, and a toner image is formed on the surface of the image carrier. The toner image formed on the image carrier is transferred on a transfer material (recording medium) by a transfer apparatus. Then, the toner image is heated by a fixing apparatus and fixed on the transfer material. Further, residual transferring toner remaining on the surface of the image carrier is removed by a cleaning apparatus, and collected in a prescribed collecting section. Residual charge on the surface of the image carrier that has been cleaned is also removed by a charge removal apparatus. Thus, the image forming apparatus is prepared for next image forming.
In general, a one-component developer that is mainly composed of toner and a two-component developer that is mainly composed of toner and a carrier are used as developer that develops an electrostatic latent image on an image carrier. Since a carrier is not used in the one-component developer, a stirring mechanism for uniformly mixing toner and a carrier and the like are not necessary. Thus, there is an advantage in that the development apparatus can be made simple; however, there is a disadvantage in that a stable charging level in the toner is difficult to obtain, and the like. Accordingly, in general, the two-component developer is often used in a high-speed image forming apparatus and a color image forming apparatus.
On the other hand, as for the two-component developer, when a toner content rate in the developer (hereinafter, referred to as toner concentration) changes on the developer carrier, image density also changes in a portion in which the toner concentration has been changed. Thus, it is necessary for a development apparatus that uses the two-component developer to develop an image carrier using developer that always has a constant toner concentration. Therefore, in order to make the toner concentration constant in the development apparatus, the developer carrier supplies toner onto the surface of the image carrier after sufficiently stirring the two-component developer (carrier and toner).
However, toner is consumed as it is provided for developing and, thus, the two-component developer includes a portion in which the toner concentration has been changed. Then, if the developer is again provided for developing from the developer carrier to the surface of the image carrier, but without being separated from the surface of the developer carrier, image failure in that image density is uneven on a portion in which the toner concentration has been changed, what is known as a development memory problem, occurs.
To address this problem, for example, JP2000-321870A (Patent Document 1) discloses a development apparatus that is provided with a scraper for scraping a two-component developer from the surface of a developer carrier, so that the developer on the developer carrier that is once provided for development on the surface of an image carrier and whose toner is consumed is not provided again, by preventing it from making one revolution together with the rotation of the developer carrier.
However, if the development apparatus is provided with the scraper as disclosed in the aforementioned Patent Document 1, problems will arise. For example, a toner aggregate is likely to occur at a front end portion of the scraper, and image irregularity is likely to occur caused by filming of a toner component on the surface of the developer carrier.